Technical Abstract:
Formulation research has the potential to improve efficacy for microbial biopesticides by addressing specialized issues concerning application and residual activity. Fungi, such as Beauveria bassiana, have a sufficiently wide-host range to make them attractive for commercial development. However, the conidia of this microbe are strongly hydrophobic, and thus provide unique challenges for formulation. Also, these conidia are susceptible to degradation when exposed to sunlight. SoyScreen is a sunscreen made by combining molecules of soy oil with ferulic acid. Ferulic acid is a natural substance in rice, oats, and other plants that absorb UV light. Conidia stored in SoyScreen oil for 6 months at 25, 30, and 35 degrees C retained viability as well as conidia stored in sunflower oil indicating that SoyScreen did not adversely affect viability. When samples were placed on glass and exposed to simulated sunlight (xenon light), conidia in SoyScreen oil retained viability better than conidia in sunflower oil or exposed without oil. However, when conidia in a SoyScreen oil formulation were applied to field grown cabbage plants, insecticidal activity against Trichoplusia ni larvae was not different when compared with unformulated conidia applied with water. We believed the benefit of the oil was lost because the oil was absorbed by the leaf, leaving the conidia exposed to sunlight. Subsequent laboratory exposures with oil formulations applied to balsa wood demonstrated this effect. As a result, additional formulation techniques will be required to prevent separation of the protective oil from the conidia when applied in the field.